npm-testdata: bump prettier from 2.8.8 to 3.0.3 in /testdata

Bumps [prettier](https://github.com/prettier/prettier) from 2.8.8 to 3.0.3.
- [Release notes](https://github.com/prettier/prettier/releases)
- [Changelog](https://github.com/prettier/prettier/blob/main/CHANGELOG.md)
- [Commits](prettier/prettier@2.8.8...3.0.3)

---
updated-dependencies:
- dependency-name: prettier
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

testdata/package.json

@@ -9,6 +9,6 @@
     "author": "Matteo Agnoletto",
     "license": "MIT",
     "devDependencies": {
-        "prettier": "^2.8.8"
+        "prettier": "^3.0.3"
     }
 }